The present invention relates generally to human dietary supplements and more specifically to dietary supplements which are useful as a source of dietary nitrogen.
Daily acquisition of sufficient dietary protein of adequate quality is an essential task of all living things. Nitrogen is a critical element required for the synthesis of protein, and a tremendous amount of human work is devoted to the effort to support the biological nitrogen economy of the species. At all stages in the existence of humans, there is a continuing process of acquisition and loss of nitrogen with nitrogen balance being the difference between intake and loss of nitrogen. Growth during infancy and childhood is characterized by a strong positive nitrogen balance in which intake substantially exceeds output. Maximal negative nitrogen balance is elicited by starvation and implies loss of lean body mass through breakdown of endogenous protein. In all mammals, maintenance of appropriate nitrogen balance equilibrium is a basic biological requirement which is ultimately dependent on timely consumption of sufficient amounts of foods of suitable nutritional quality.
In humans as in other mammals, a reserve of non-protein nitrogen is provided by urea, a compound ubiquitous in the blood of mammals. Blood urea nitrogen (BUN) is routinely measured as a critical indicator in human medicine. There is a direct relationship between BUN and the total nitrogen balance in humans when BUN is less than about 14 mg/100 ml of blood serum.
Protein malnutrition is known to be closely related to energy malnutrition such that protein-energy malnutrition is known as a single syndrome. Ethanol (grain alcohol) is high in calories; that is, it is a rich source of dietary energy. Ethanol, however, is known to be functionally distinct from energy sources such as glucose and other carbohydrates with respect to nitrogen metabolism even though it does not itself contain nitrogen. Specifically, parenteral infusions yielding 15 cc of 98% ethanol per hour have been found to induce positive nitrogen retention despite a negative energy balance. Moreover, a strong and consistent nitrogen balance is attained with ethanol infusion if adequate energy is available from extraneous sources. Nevertheless, while ethanol is known to induce a positive nitrogen balance, there are numerous health and social concerns regarding alcohol consumption which render ethanol undesirable as an agent to promote nitrogen retention.
Industrially synthesized urea has long been recognized to be a potentially valuable source of supplementary nitrogen for the diet. For example, studies have shown that the simple addition of urea to diets deficient in "unessential" nitrogen will restore a positive nitrogen balance in human subjects. Of interest to the present application is U.S. Pat. No. 2,803,332 which discloses feed supplements for ruminants which contain urea and ethanol in amounts which increase the nitrogen retention ability of the animal. While addition of ethanol to drinking water in the amount of 1.33% ethanol with low protein rations will cause intoxication in cattle, ethanol intoxication of livestock fed the urea/ethanol supplement of U.S. Pat. No. 2,803,332 has not been reported.
The widespread use of urea as a source of human dietary nitrogen has been prevented by the hazards of the "urea toxicity syndrome" as well as by the general unavailability of sufficiently pure edible urea which is free of the toxic contaminant biuret. A further problem with the use of urea as a human dietary supplement relates to the inefficiency with which the non-protein urea nitrogen may be converted to protein in vivo. In other words, the biological value of urea per se may be relatively low compared to usual dietary sources of protein. In general, urea nitrogen is not retained when dietary protein is otherwise available. This situation changes when dietary protein is deficient, indicating the role of urea as a "reserve" source of nitrogen for amino acid (and hence protein) synthesis.